New member here. I bought a C658 the day it came into the dealer. I don't know anything about the difference in chipset quality, so hopefully they did OK with this unit. I AB'd this against an NAD M12 at the dealer - I have to say the M12 was a better sounding unit, but the longer I've been doing this, I've gotten more realistic about how this system is going to be used and thought the C658 would do just fine. I used to spend a lot (for me) trying to shore up the weak links in my system - with every big purchase, I was immediately looking for the next project. At the height of it, I had Genesis V speakers, Pass Lab X1 preamp and X250 amp, etc., and was still unsatisfied. I then went the AV route so the family could enjoy it, sold the Gens and Pass Lab stuff, and have been without a good 2-channel preamp for a long time, and really have not spent much time listening to music on anything other than headphones. Anyway, this is a very long-winded way of saying that while there may be better sounding units out there, you're going to pay substantially more for them. This thing does what I need it to do. It sounds very good pulling music from my NAS unit or CD player and absolutely wonderful streaming high-def stuff straight from the interwebs.
I am a newbie to this whole streaming/wireless/BT thing in my audio, so perhaps this is common; the NAD is very cranky about how you set it up. The initial update had to be done via ethernet, and surprisingly (to me) the wireless setup had to be done that way, too. Also, it did not like when I tried to rename the "room" in the BluOS app, and would not recognize the network until I changed it back to "living room". We recently swapped over to a mesh-wifi system, and that was a PITA to reestablish my setup - again, the NAD had to be pulled out of the rack and hooked directly to an ethernet cable to get it to work. Outside of that, I am very happy with it. It's great being able to control everything from my phone. The NAD is in constant standby mode, and wakes the amp via a 12v trigger, so no switches to throw. I've been a little frustrated with the inability to get the Dirac program to run, but after stumbling into this forum, I now know it isn't available yet - looking forward to experimenting with that.
Overall, this is a much cleaner setup with very high WAF.